Answer
$[x(x+40)] \text{ square inches}$
Work Step by Step
The amount of material needed to construct the bottom of the box is $x^2.$
The amount of material needed to construct one side of the box is $10x.$ With $4$ sides in a box, then the total amount of material to construct all the sides of the box is $40x.$
Adding the bottom and side parts of the box, the total amount of material to construct the box is
\begin{array}{l}\require{cancel}
x^2+40x
\\=
x(x+40)
.\end{array}
Hence, the amount of material to construct the box is $
[x(x+40)] \text{ square inches}
.$
